US District Judge Lynwood Smith imposed the sentence on Jarvis M Britton during a hearing today in Huntsville.
Britton must spend three years on probation after finishing the prison term.
The 26-year-old Birmingham man pleaded guilty in March to threatening the president's life. Prosecutors say Britton sent a tweet in September that said, "Let's kill the president. F.E.A.R."
Several people have been linked to a national militia group that prosecutors say was called F.E.A.R. It stands for Forever Enduring Always Ready.